Yes, but the weight of the water on the glass as the depth increases will be much more immediately important than any variations in bouancy brought on by respiration.
I prefer to think of this not so much as a calculus problem, but a phys ed one- can you get the window or door open, and then not die while attempting to swim to shore.
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-IronRaven
When a man dare not speak without malice for fear of giving insult, that is when truth starts to die. Truth is the truest freedom.